Illumination device, display device, and method of manufacturing light modulator

ABSTRACT

An illumination device is provided and has a light guide plate, a light source and a light modulator, wherein the light modulator has a pair of transparent substrates a pair of electrodes and a light modulator layer. The light modulator layer includes a first region being changed between a transparent state and a scatterable state depending on intensity of an electric field, and a second region being more transparent than the first region in a scatterable state at an electric field having a certain intensity, the electric field being applied when the first region is changed between the transparent state and the scatterable state, and an occupancy rate of the first region in the light modulator layer is increased with increase in distance from the light source.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.12/644,820, filed Dec. 22, 2009, which claims priority to JapanesePriority Patent Application JP 2008-334658 filed in the Japan PatentOffice on Dec. 26, 2008, the entire content of which is herebyincorporated by reference.

BACKGROUND

The present disclosure relates to an illumination device and a displaydevice, each device having a light modulator that may scatter ortransmit light, and a method of manufacturing the light modulator.

Recently, a liquid crystal display is remarkably improved in imagequality or remarkably advanced in power saving, and a method is proposedto improve scotopic contrast, where the contrast is improved bypartially modulating intensity of light from a backlight. The method islargely designed to partially drive light emitting diodes (LED) as alight source of a backlight so that light from the backlight ismodulated in accordance with a display image. Furthermore, thicknessreduction is now increasingly demanded not only to a small liquidcrystal display, but also to a large liquid crystal display. Therefore,an edge light type of backlight, where a light source is disposed at anend of a light guide plate, is noted instead of a backlight type where acold cathode fluorescent lamp (CCFL) or LED is disposed directly below aliquid crystal panel. However, the edge light type is hard to enablepartial drive of partially modulating light intensity of a light source.

For example, Japanese Unexamined Patent Application, Publication No.6-347790 proposes a display device using a polymer dispersed liquidcrystal (PDLC), which is changed between a transparent state and ascatterable state, as a technique of extracting light being propagatedthrough the light guide plate. This is a technique for preventingmirroring, where voltage is partially applied to the PDLC so that thePDLC is partially changed between the transparent state and thescatterable state.

In the edge light backlight, for example, a technique is known, in whicha printing pattern, coarseness of a light extraction pattern, or size ofa pattern is changed depending on a distance from a light source such asLED or CCFL (for example, refer to Japanese Unexamined PatentApplication, Publication No. 11-142843). The technique described in thePatent Application is a kind of technique for uniformly extracting lightfrom a light guide plate, and designed only in consideration of lightextraction. In addition, for example, a technique is known as atechnique for making luminance uniform in a plane, in which lightdiffusivity of a diffuser sheet is gradually changed in accordance witha distance from a light source (for example, refer to JapaneseUnexamined Patent Application, Publication No. 2004-253335).

For example, it is considered that the technique of the PatentApplication, Publication No. 11-142843 or 2004-253335 is combined withthe PDLC of the Patent Application, Publication No. 6-347790 so thatluminance of light from the backlight is made uniform in a plane.However, in such a case, while luminance may be made uniform, luminancein dark display is increased, resulting in a difficulty that amodulation ratio between bright display luminance and dark displayluminance may not be increased.

It is desirable to provide an illumination device and a display device,in which a modulation ratio may be increased while luminance is madeuniform in a plane, and a method of manufacturing a light modulator.

SUMMARY

An illumination device according to an embodiment includes a light guideplate, a light source disposed on a side face of the light guide plate,and a light modulator being disposed on a surface or in the inside ofthe light guide plate, and being adhered to the light guide plate. Thelight modulator has a pair of transparent substrates separately disposedin an opposed manner to each other, a pair of electrodes provided onrespective surfaces of the pair of transparent substrates, and a lightmodulator layer provided in a gap between the pair of transparentsubstrates. The light modulator layer includes a first region beingchanged between a transparent state and a scatterable state depending onintensity of an electric field, and a second region being moretransparent than the first region in a scatterable state at an electricfield having a certain intensity, the electric field being applied whenthe first region is changed between the transparent state and thescatterable state. An occupancy rate of the first region in the lightmodulator layer is increased with increase in distance from the lightsource.

A display device according to an embodiment includes a display panelhaving a plurality of pixels arranged in a matrix pattern, the pixelsbeing driven according to an image signal, and an illumination deviceilluminating the display panel. The illumination device incorporated inthe display device has the same configuration as that of the aboveillumination device.

According to the illumination device and the display device of theembodiments, the light modulator layer is provided in the lightmodulator adhered to the light guide plate, the light modulator layerincluding the first region being changed between a transparent state anda scatterable state depending on intensity of an electric field, and thesecond region being more transparent than the first region in ascatterable state at an electric field having a certain intensity, theelectric field being applied when the first region is changed betweenthe transparent state and the scatterable state. Thus, light, which isemitted from the light source, and propagated through the light guideplate, is transmitted through a region being transparent by controllingan electric field, and perfectly reflected or reflected at a highreflectance by an interface of one transparent substrate. As a result,luminance of a region corresponding to a region being transparent in alight emitting area of the illumination device (hereinafter, simplyreferred to as transparent region in the light emitting area) isdecreased compared with a case where the light modulator is notprovided. In contrast, light propagated through the light guide plate isscattered by a region, which has light-scattering ability by controllingan electric field, of the light modulator layer, and transmitted throughthe interface of the transparent substrate. As a result, luminance of aregion corresponding to a region that has light-scattering ability inthe light emitting area of the illumination device (hereinafter, simplyreferred to as scattering region in the light emitting area) isincreased compared with the case where the light modulator is notprovided. In addition, partial white-display luminance (luminance raise)is increased by a level corresponding to decrease in luminance of thetransparent region in the light emitting area. Furthermore, according tothe embodiments of the invention, an occupancy rate of the first regionin the light modulator layer is increased with increase in distance fromthe light source. Thus, luminance on a light source side of the lightemitting area of the illumination device is controlled to be lowcompared with the case where the light modulator is not provided, andluminance on a side opposite to the light source side of the lightemitting area of the illumination device is increased compared with thecase where the light modulator is not provided.

A method of manufacturing a light modulator according to an embodimentincludes the following two steps.

(A) A first step of disposing two transparent substrates, eachtransparent substrate having an electrode and an alignment film formedsequentially on its surface, such that respective alignment films areopposed to each other, and attaching the transparent substrates to eachother with a mixture of a liquid crystal material and a polymerizablematerial in between, and then disposing a mask on the attachedtransparent substrates, the mask having an open area ratio varyingdepending on a distance from a region where a light source is to bedisposed.

(B) A second step of irradiating light to the polymerizable material viathe mask to polymerize the polymerizable material, thereby forming afirst region being changed between a transparent state and a scatterablestate depending on intensity of an electric field, and a second regionbeing more transparent than the first region in a scatterable state atan electric field having a certain intensity, the electric field beingapplied when the first region is changed between the transparent stateand the scatterable state.

According to the method of manufacturing a light modulator of theembodiment, the mixture of a liquid crystal material and a polymerizablematerial is provided between the two transparent substrates, and thenlight is irradiated to the polymerizable material. Thus, thepolymerizable material is polymerized, and besides, the liquid crystalmaterial and the polymerizable material are phase-separated from eachother. The light is irradiated to the polymerizable material via themask. Therefore, the first region being changed between a transparentstate and a scatterable state depending on intensity of an electricfield, and a second region being more transparent than the first regionin a scatterable state at an electric field having a certain intensity,the electric field being applied when the first region is changedbetween the transparent state and the scatterable state are formed inaccordance with intensity of irradiated light and a mask pattern.Moreover, the mask varies in open area ratio depending on a distancefrom a region where the light source is to be disposed. Therefore, anoccupancy rate of the first region in the mixture may be varieddepending on the distance from the region where the light source is tobe disposed. In this way, according to the embodiment of the invention,light irradiation using the mask enables that the first and secondregions are formed in the mixture with an occupancy rate depending onthe distance from the region where the light source is to be disposed.

When the light modulator formed in this way is applied to anillumination device of a light guide plate type, light, which is emittedfrom the light source, and propagated through the light guide plate, istransmitted through a region being transparent by controlling anelectric field, and perfectly reflected or reflected at a highreflectance by the interface of one transparent substrate. As a result,luminance of the transparent region in the light emitting area may bedecreased compared with the case where the light modulator is notprovided. In contrast, light propagated through the light guide plate isscattered by a region, which has light-scattering ability by controllingan electric field, of the mixture, and transmitted through the interfaceof the transparent substrate. Thus, luminance of the scattering regionin the light emitting area may be increased compared with the case wherethe light modulator is not provided. In addition, partial white-displayluminance may be increased by a level corresponding to decrease inluminance of the transparent region in the light emitting area.Moreover, luminance on a light source side of the light emitting areamay be controlled to be low compared with the case where the lightmodulator is not provided, and luminance on a side opposite to the lightsource side of the light emitting area may be increased compared withthe case where the light modulator is not provided.

According to the illumination device, the display device and the methodof manufacturing a light modulator of the embodiments, luminance on alight source side of the light emitting area of the illumination devicemay be controlled to be low compared with the case where the lightmodulator is not provided, and luminance on a side opposite to the lightsource side of the light emitting area of the illumination device may beincreased compared with the case where the light modulator is notprovided. Thus, a modulation ratio may be increased while luminance ismade uniform in a plane.

According to the method of manufacturing a light modulator of theembodiment, light irradiation using the mask enables that the first andsecond regions are formed in the mixture with an occupancy ratedepending on a distance from the region where the light source is to bedisposed. Thus, a light modulator having uniform luminance in a planeand a high modulation ratio may be manufactured by a simple method.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B are section views showing an example of a configurationof a backlight according to a first embodiment of the invention.

FIG. 2 is a section view showing an example of a configuration ofelectrodes in FIG. 1.

FIG. 3 is a section view showing another example of the configuration ofthe backlight in FIG. 1.

FIG. 4 is a plan view showing an example of a top configuration of alight modulator in FIG. 1.

FIG. 5 is a relationship diagram showing an example of a relationshipbetween voltage and transmittance in each of first and second regions ofthe light modulator in FIG. 1.

FIGS. 6A and 6B are schematic views for illustrating an example ofoperation of the first region in FIG. 5.

FIGS. 7A and 7B are schematic views for illustrating an example ofoperation of the second region in FIG. 5.

FIG. 8 is a relationship diagram showing another example of therelationship between voltage and transmittance in each of the first andsecond regions of the light modulator in FIG. 1.

FIGS. 9A and 9B are schematic views for illustrating an example ofoperation of the second region in FIG. 8.

FIGS. 10A and 10B are schematic views for illustrating another exampleof the operation of the second region in FIG. 8.

FIG. 11 is a relationship diagram showing still another example of therelationship between voltage and transmittance in each of the first andsecond regions of the light modulator in FIG. 1.

FIGS. 12A and 12B are schematic views for illustrating an example ofoperation of the second region in FIG. 11.

FIGS. 13A and 13B are schematic views for illustrating operation of thebacklight of FIG. 1.

FIGS. 14A to 14C are section views for illustrating manufacturing stepsof the backlight of FIG. 1;

FIGS. 15A to 15C are section views for illustrating manufacturing stepssubsequent to FIGS. 14A to 14C.

FIGS. 16A to 16C are section views for illustrating manufacturing stepssubsequent to FIGS. 15A to 15C.

FIGS. 17A to 17D are characteristic diagrams for illustrating frontluminance of the backlight of FIG. 1.

FIG. 18 is a section view showing still another example of theconfiguration of the backlight of FIG. 1;

FIG. 19 is a section view showing still another example of theconfiguration of the backlight of FIG. 1.

FIG. 20 is a section view showing still another example of theconfiguration of the backlight of FIG. 1.

FIGS. 21A and 21B are section views showing an example of aconfiguration of a backlight according to a second embodiment.

FIG. 22 is a relationship diagram showing an example of a relationshipbetween voltage and transmittance in each of first and second regions ofa light modulator in FIG. 21.

FIGS. 23A and 23B are schematic views for illustrating an example ofoperation of the first region in FIG. 22.

FIGS. 24A and 24B are schematic views for illustrating an example ofoperation of the second region in FIG. 22.

FIG. 25 is a relationship diagram showing another example of therelationship between voltage and transmittance in each of the first andsecond regions of the light modulator in FIG. 21.

FIGS. 26A and 26B are schematic views for illustrating an example ofoperation of the second region in FIG. 25.

FIGS. 27A and 27B are schematic views for illustrating another exampleof the operation of the second region in FIG. 25.

FIG. 28 is a relationship diagram showing still another example of therelationship between voltage and transmittance in each of the first andsecond regions of the light modulator in FIG. 21.

FIGS. 29A and 29B are schematic views for illustrating an example ofoperation of the second region in FIG. 28.

FIGS. 30A and 30B are schematic views for illustrating another exampleof the operation of the second region in FIG. 28.

FIG. 31 is a section view showing an example of a display deviceaccording to an application example.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described in detail with reference todrawings. Description is made in the following order.

1. First embodiment (backlight, normally-white PDLC)

2. Modification (position of light modulator, addition of optical sheet)

3. Second embodiment (backlight, reverse PDLC)

4. Application example (display device)

First Embodiment

FIG. 1A shows an example of a sectional configuration of a backlight 1(illumination device) according to a first embodiment. FIG. 1B shows anexample of a sectional configuration of a light modulator 30 (describedlater) incorporated in the backlight 1 of FIG. 1A. FIGS. 1A and 1Bschematically show the examples, and therefore a dimension or shape isnot limited to be the same as an actual dimension or shape in thefigures. The backlight 1, for example, illuminates a liquid crystaldisplay panel from the back of the panel, and includes a light guideplate 10, a light source 20 disposed on a side face of the light guideplate 10, a light modulator 30 and a reflector plate 40, which aredisposed in the back of the light guide plate 10, and a drive circuit 50driving the light modulator 30.

The light guide plate 10 guides light from the light source 20, which isdisposed on the side face of the light guide plate 10, to a top of thelight guide plate 10. The light guide plate 10 has a shape incorrespondence to a display panel (not shown) disposed on the top of thelight guide plate 10, for example, a rectangular prism shape enclosed bythe top, a bottom and side faces. For example, the light guide plate 10has a predetermined, patterned shape on at least one of the top and thebottom, and thus has a function of scattering light injected from theside face, and uniforming the light. The light guide plate 10 need notnecessarily have the shape, and, for example, may have athree-dimensional shape enclosed by flat surfaces. For example, thelight guide plate 10 even acts as a supporter supporting an opticalsheet (for example, a diffuser plate, a diffuser sheet, a lens film, anda polarization separation sheet). For example, the light guide plate 10mainly includes transparent thermoplastic resin such as polycarbonateresin (PC) or acrylic resin (polymethylmethacrylate (PMMA)).

The light source 20 is a linear light source, and for example, includesa hot cathode fluorescent lamp (HCFL), CCFL, or a plurality of LEDarranged in a line. The light source 20 may be provided on only one sideface of the light guide plate 10 as shown in FIG. 1A, or may be providedon two, three or all side faces of the light guide plate 10.

The reflector plate 40 returns light, which is leaked from the back ofthe light guide plate 10 via the light modulator 30, to a side of thelight guide plate 10, and for example, has a function of reflecting,diffusing, or scattering the light. Thus, light emitted from the lightsource 20 may be efficiently used, and besides front luminance isincreased. The reflector plate 40, for example, includes PET(polyethylene terephthalate) foam, a silver-evaporated film, amultilayer reflection film, or white PET.

In the embodiment, the light modulator 30 adheres to the back (bottom)of the light guide plate 10 without inserting an air layer, and isbonded to the back of the plate 10 via an adhesive (not shown) or thelike. The light modulator 30 is, for example, formed by disposing atransparent substrate 31, a lower electrode 32, an alignment film 33, alight modulator layer 34, an alignment film 35, an upper electrode 36and a transparent substrate 37 in order from a side of the reflectorplate 40 as shown in FIG. 1B.

The transparent substrate 31 or 37 supports the light modulator layer34, and typically includes a substrate transparent to visible light, forexample, a glass plate or a plastic film. The lower electrode 32 isprovided on a surface of the transparent substrate 31, the surface beingopposed to the transparent substrate 37, and for example, has a beltlikeshape extending in one direction in a plane as shown in FIG. 2 showing arelevant part of the light modulator 30. The upper electrode 36 isprovided on a surface of the transparent substrate 37, the surface beingopposed to the transparent substrate 31, and for example, has a beltlikeshape extending in one direction in a plane, the direction beingcorresponding to a direction intersecting with (perpendicular to) theextending direction of the lower electrodes 32, as shown in FIG. 2.

The upper and lower electrodes 32 and 36 are shaped in connection with adrive method. For example, when the electrodes have the beltlike shaperespectively, the electrodes may be driven by a simple matrix drive.When one of the electrodes is shaped to be a solid film, and the otheris shaped to be small squares, the electrodes may be driven, forexample, by an active matrix drive.

In the upper and lower electrodes 32 and 36, at least the upperelectrode 36 (electrode on a top side of the backlight 1) includes atransparent conductive material, for example, indium tin oxide (ITO).However, the lower electrode 32 (electrode on a bottom side of thebacklight 1) may not include a transparent material, and may includemetal or the like. When the lower electrode 32 includes metal, the lowerelectrode 32 further has a function of reflecting light incident to thelight modulator 30 from the back of light guide plate 10 as performed bythe reflector plate 40. In this case, for example, the reflector plate40 may not be provided as shown in FIG. 3.

When the lower electrode 32 and the upper electrode 36 are viewed in anormal direction to the light modulator 30, portions of the lightmodulator 30 configure light modulator cells 30A, the portions beingcorresponding to regions where the upper and lower electrodes 32 and 36are opposed to each other. Each light modulator cell 30A may beindependently driven by applying a predetermined voltage between theupper and lower electrodes 32 and 36, and transmits or scatters lightfrom the light source 20 depending on a voltage value applied betweenthe electrodes. Such transmitting or scattering behavior of the cell isdescribed in detail in conjunction with description of the lightmodulator layer 34.

The alignment film 33 or 35 is provided, for example, to align a liquidcrystal or monomer used for the light modulator layer 34. While thealignment film includes, for example, a vertical alignment film and ahorizontal alignment film, the vertical alignment film is preferablyused for the alignment film 33 or 35. For the vertical alignment film, asilane coupling agent, polyvinyl alcohol (PVA), a polyimide seriesmaterial, a surfactant or the like may be used. These materials need notbe subjected to rubbing processing for forming the alignment film, andis thus excellent in dust or static electricity. When a plastic film isused for the transparent substrate 31 or 37, baking temperature ispreferably low to the utmost after the alignment film 33 or 35 is coatedon a surface of the transparent substrate 31 or 37 in a manufacturingprocess, the silane coupling agent is preferably used for the alignmentfilm 33 or 35 because alcohols may be used for the agent.

It is enough for either of the vertical and horizontal alignment filmsto have a function of aligning a liquid crystal and a monomer, and it isnot necessary for the alignment films to have reliability to repeatedvoltage application being desired for a typical liquid crystal display.This is because the reliability to voltage application to a produceddevice is determined by an interface condition between a polymerizedproduct of the monomer and the liquid crystal. Moreover, even if thealignment film is not used, a liquid crystal or a monomer used for thelight modulator layer 34 may be aligned, for example, by applying anelectric field or a magnetic field between the lower and upperelectrodes 32 and 36. That is, while an electric field or a magneticfield is applied between the lower and upper electrodes 32 and 36, analignment condition of the liquid crystal or the monomer under a voltageapplied condition may be fixed by irradiating ultraviolet rays. Whenvoltage is used for forming the alignment film, an alignment electrodeand a drive electrode are separately formed, or a two-frequency liquidcrystal, the dielectric constant of which reverses depending onfrequency, may be used as the liquid crystal material. When a magneticfield is used for forming the alignment film, a material having a largemagnetic susceptibility is preferably used for the alignment film, andfor example, a material having many benzene rings is preferably used.

The light modulator layer 34 has, for example, two regions (first region34A and second region 34B) different in optical characteristic at acertain electric-field intensity as shown in FIG. 1B. The first region34A and the second region 34B have, for example, a columnar shapeextending in a stacking direction of the light modulator 30respectively. The first region 34A is, for example, formed filling theperiphery of the second region 34B as shown in FIG. 2, and the secondregion 34B is dispersed within the first region 34A as viewed from a topof the light modulator layer 34.

The second region 34B has, for example, a cylindrical shape, anelliptical cylinder shape, or a prismatic shape. For example, diameterof the second region 34B is constant regardless of a distance from thelight source 20, and for example, about several micrometers to severalmillimeters. The diameter of the second region 34B need not benecessarily constant, and, for example, may be decreased with increasein distance from the light source 20. When the diameter of the secondregion 34B is constant, an occupancy rate (density) of the second region34B in the light modulator layer 34 is, for example, decreased withincrease in distance from the light source 20 as shown in FIGS. 1B and4. When the diameter of the second region 34B is decreased with increasein distance from the light source 20, number of the second region 34Bper area is set such that an occupancy rate (density) of the region 34Bin the light modulator layer 34 is decreased with increase in distancefrom the light source 20. Consequently, in each case, an occupancy rateof the first region 34A in the light modulator layer 34 is constant in athickness direction, and increased with increase in distance from thelight source 20 in an in-plane direction.

The first region 34A and the second region 34B need not necessarily havea columnar shape. For example, when the first region 34A has a bulkshape, and the second region 34B has a block shape, the light modulatorlayer 34 may be configured such that the second region 34B is dispersedin the first region 34A not only in an in-plane direction but also in athickness direction. When the second region 34B is uniformly dispersedin the thickness direction, and dispersed more thinly with increase indistance from the light source 20 in an in-plane direction, an occupancyrate of the first region 34A in the light modulator layer 34 is the samein a thickness direction, and increased with increase in distance fromthe light source 20 in an in-plane direction. When the second region 34Bis nonuniformly dispersed in the thickness direction, and dispersed morethinly with increase in distance from the light source 20 in an in-planedirection, an occupancy rate of the first region 34A in the lightmodulator layer 34 varies in a thickness direction, and is increasedwith increase in distance from the light source 20 in an in-planedirection.

The first region 34A includes, for example, a bulk 38A (third region)and fine particles 39A (fourth region). Similarly, the second region 34Bincludes, for example, a bulk 38B (fifth region) and fine particles 39B(sixth region). The fine particles 39A is fast in response speed to anelectric field compared with the bulk 38A. Similarly, the fine particles39B is fast in response speed to an electric field compared with thebulk 38B.

The bulk 38A or 38B is formed by curing an isotropic low-molecularmaterial (for example, ultraviolet curing resin or thermosetting resinbeing nondirectional to the alignment film 33 or 35), and includes apolymeric material isotropic to light from the light source 20. The bulk38A or 38B has, for example, a streaky or porous structure nonrespondentto an electric field. In contrast, the fine particles 39A or 39B mainlyinclude, for example, a liquid crystal material. When the fine particlesare applied with an electric field having certain intensity, the fineparticles align in an electric field direction, and resultantly becomeoptically anisotropic. When the fine particles are not applied with anelectric field, the fine particles become optically isotropic. That is,the fine particles 39A or 39B become optically isotropic when they arealigned unlike the bulk 38A or 38B.

A weight ratio W1 between the fine particles 39A and the bulk 38A(weight of the fine particles 39A/weight of the bulk 38A) is differentfrom a weight ratio W2 between the fine particles 39B and the bulk 38B(weight of the fine particles 39B/weight of the bulk 38B). Specifically,the weight ratio W2 is smaller than the weight ratio W1. The weightratio W1 is, for example, 95/5 to 65/35, and the weight ratio W2 is, forexample, 5/95 to 35/65. When the weight ratio W2 is within theexemplified range, the second region 34B may act as spacers for keepinga cell gap.

In the embodiment, both the first and second regions 34A and 34B areconfigured such that, depending on electric-field intensity, an opticalaxis of each of the fine particles 39A and 39B, for example, becomesperpendicular to a surface (hereinafter, called reference surface)parallel to a surface of each of the transparent substrates 31 and 37,or intersects with the surface at a shallow angle. Thus, each of thefirst and second regions 34A and 34B may be changed between atransparent state and a scatterable state as described later. However, avoltage for changing the first region 34A between the transparent stateand the scatterable state, and a voltage for changing the second region34B between the transparent state and the scatterable state aredifferent from each other depending on a magnitude relationship betweenthe weight ratios W1 and W2.

Hereinafter, an optical characteristic of each of the first and secondregions 34A and 34B is described in detail while being classified intothree cases. The classification is made focusing on three factors of (1)particle diameter of the fine particles 39B, (2) magnitude relationshipbetween the weight ratios W1 and W2, and (3) an occupancy rate of thefine particles 39B in the second region 34B.

Case 1

In this case, particle diameter of the fine particles 39B is larger thanthat of the fine particles 39A, so that a liquid crystal in the fineparticles 39B easily moves compared with a liquid crystal in the fineparticles 39A. As a result, for example, a drive start voltage V2 of thesecond region 34B is lower than a drive start voltage V1 of the firstregion 34A as shown in FIG. 5. FIG. 5 schematically shows a relationshipbetween applied voltage and transmittance in each of the first andsecond regions 34A and 34B.

In the case 1, particle diameter of the fine particles 39B is largerthan that of the fine particles 39A, and besides, the weight ratio W2 issmaller than the weight ratio W1. Therefore, the second region 34B has alow light-scattering ability during voltage application. As a result, asshown in FIG. 5, when the drive start voltage V1 is applied betweenelectrodes, transmittance of the second region 34B is somewhat high, andthe second region 34B is thus substantially transparent. In the case 1,a drive range defined as a range of a lower limit voltage V_(min) to anupper limit voltage V_(max) is, for example, set as V1 to V3, therebythe second region 34B may be kept to be transparent or substantiallytransparent while the first region 34A is changed between a transparentstate and a scatterable state. The drive range may be a range other thanthe above, and, for example, may be 0 (zero) to V3. Hereinafter, anoptical characteristic of each region in the case 1 is described.

FIG. 6A schematically shows optical operation of the first region 34A inthe case that the drive start voltage V1 of the first region 34A isapplied as the lower limit voltage V_(min) between electrodes. In thiscase, the bulk 38A is isotropic, and is not aligned. FIG. 6Bschematically shows optical operation of the first region 34A in thecase that a saturation voltage V3 of the first region 34A is applied asthe upper limit voltage V_(max) between electrodes. FIG. 7Aschematically shows optical operation of the second region 34B in thecase that the drive start voltage V1 is applied as the lower limitvoltage V_(min), between electrodes. In this case, the bulk 38B isoptically isotropic, and is not aligned. FIG. 7B schematically showsoptical operation of the second region 34B in the case that thesaturation voltage V3 is applied as the upper limit voltage V_(max)between electrodes.

When the drive start voltage V1 is applied between electrodes, forexample, the liquid crystal in the fine particles 39A or 39B is orientedin a random direction regardless of a direction of an electric field E1,and thus not aligned as shown in FIGS. 6A and 7A. That is, the fineparticles 39A or 39B are optically isotropic. In contrast, when thesaturation voltage V3 is applied between electrodes, for example, theliquid crystal in the fine particles 39A or 39B is oriented in the sameor approximately the same direction as a direction of an electric fieldE2, and thus aligned in a direction (hereinafter, simply called verticaldirection) perpendicular to a surface of the transparent substrate 31 or37 as shown in FIGS. 6B and 7B. That is, the fine particles 39A or 39Bare optically anisotropic. In such a case, a light axis (line parallelto a forward direction of a beam, along which a refractive index has onevalue regardless of a polarization direction) of the liquid crystal inthe fine particles 39A or 39B is oriented in the vertical direction. Thelight axis of the liquid crystal in the fine particles 39A or 39B neednot be necessarily oriented in the vertical direction, and, for example,may be oriented in a direction intersecting with the vertical directiondue to manufacturing errors or the like.

A refractive index of the bulk 38A or 38B is different from a refractiveindex of the fine particles 39A or 39B when the fine particles areoptically isotropic. A refractive index of the bulk 38A is equal to orapproximately equal to an extraordinary index of the fine particles 39Aor 39B when the fine particles are optically anisotropic.

In the first region 34A, when the drive start voltage V1 is appliedbetween electrodes, a difference in refractive index between the bulk38A and the fine particles 39A is large in any direction. As a result,the first region 34A has a high light-scattering ability as shown inFIG. 6A. In contrast, in the second region 34B, for example, particlediameter of the fine particles 39B is larger than particle diameter ofthe fine particles 39A as shown in FIG. 7A, so that the liquid crystalin the fine particles 39B easily moves compared with the liquid crystalin the fine particles 39A. Thus, an orientation of the liquid crystal,which has been oriented in a random direction in the fine particles 39B,is displaced only slightly in the vertical direction by applying thedrive start voltage V1 between electrodes, and a difference inrefractive index between the bulk 38B and the fine particles 39B is thusdecreased in each of oblique and lateral directions. As a result, thesecond region 34B becomes substantially transparent despite occurrenceof slight scattering in the region 34B as shown in FIG. 7A.

When the saturation voltage V3 is applied between electrodes,substantially no difference exists in refractive index between the bulk38A or 38B and the fine particles 39A or 39B in both oblique and lateraldirections in each of the first and second regions 34A and 34B. Thus,high transparency is obtained in both the regions as shown in FIGS. 6Band 7B.

Case 2

In this case, particle diameter of the fine particles 39B is larger thanthat of the fine particles 39A as in the case 1. As a result, forexample, a drive start voltage V2 of the second region 34B is lower thana drive start voltage V1 of the first region 34A as shown in FIG. 8.FIG. 8 schematically shows a relationship between applied voltage andtransmittance in each of the first and second regions 34A and 34B.

Furthermore, in the case 2, the weight ratio W2 is smaller than theweight ratio W1 as in the case 1, but the weight ratio W2 is smallerthan that in the case 1. As a result, for example, the drive startvoltage V2 is smaller than the drive start voltage V1, and when novoltage is applied between electrodes, transmittance of the secondregion 34B is high compared with that in the case 1, as shown in FIG. 8.That is, in the case 2, the second region 34B is substantiallytransparent during no voltage application.

In the case 2, a drive range defined as a range of a lower limit voltageV_(min) to an upper limit voltage V_(max) is, for example, set as 0(zero) to V3, thereby the second region 34B may be kept to betransparent or substantially transparent while the first region 34A ischanged between a transparent state and a scatterable state. The driverange may be a range other than the above, and, for example, may be V2to V3, or V1 to V3. Hereinafter, an optical characteristic of eachregion in the case 2 is described.

FIGS. 9A and 10A schematically show optical operation of the secondregion 34B in the case that no voltage is applied between electrodes. Inthis case, the bulk 38B is optically isotropic, and is not aligned.FIGS. 9B and 10B schematically show optical operation of the secondregion 34B in the case that the saturation voltage V3 is applied as theupper limit voltage V_(max) between electrodes.

In the case 2, for example, an occupancy rate of the bulk 38B in thesecond region 34B is large compared with that in the case 1 as shown inFIGS. 9A and 9B, or, for example, particle diameter of the fineparticles 39B is extremely large compared with that in the case 1 asshown in FIGS. 10A and 10B.

In the case 2, an internal configuration of the first region 34A is thesame as that in the case 1. Therefore, when no voltage is appliedbetween electrodes, optical operation of the first region 34A is thesame as optical operation as schematically shown in FIG. 6A. Moreover,when the saturation voltage V3 is applied as the upper limit voltageV_(max) between electrodes, optical operation of the first region 34A isthe same as optical operation as schematically shown in FIG. 6B.

When no voltage is applied between electrodes, for example, a liquidcrystal in the fine particles 39A or 39B is oriented in a randomdirection, and thus not aligned as shown in FIGS. 6A and 9A or FIG. 10A.That is, the fine particles 39A or 39B are optically isotropic. Incontrast, when the saturation voltage V3 is applied between electrodes,for example, the liquid crystal in the fine particles 39A or 39B isoriented in the same or approximately the same direction as a directionof an electric field E2, and thus aligned in the vertical direction asshown in FIGS. 6B and 9B or FIG. 10B. In such a case, the fine particles39A or 39B are optically anisotropic. At that time, a light axis of theliquid crystal in the fine particles 39A or 39B is oriented in thevertical direction. The light axis of the liquid crystal in the fineparticles 39A or 39B need not be necessarily oriented in the verticaldirection, and, for example, may be oriented in a direction intersectingwith the vertical direction due to manufacturing errors or the like.

A refractive index of the bulk 38A or 38B is different from a refractiveindex of the fine particles 39A or 39B when the fine particles areoptically isotropic. A refractive index of the bulk 38A is equal to orapproximately equal to an extraordinary index of the fine particles 39Aor 39B when the fine particles are optically anisotropic.

In the first region 34A, when the drive start voltage V1 is appliedbetween electrodes, a difference in refractive index between the bulk38A and the fine particles 39A is large in any direction. As a result,the first region 34A has a high light-scattering ability as shown inFIG. 6A. In contrast, in the second region 34B, for example, particlediameter of the fine particles 39B is larger than particle diameter ofthe fine particles 39A as shown in FIG. 9A or 10A. Furthermore, anoccupancy rate of the bulk 38B in the second region 34B is largecompared with that in the case 1, or particle diameter of the fineparticles 39B is extremely large compared with that in the case 1.Therefore, scattering in the second region 34B is reduced compared withthat in the case 1, and transmittance of the second region 34B is thushigh compared with that in the case 1. As a result, for example, thesecond region 34B becomes substantially transparent despite occurrenceof slight scattering in the region 34B as shown in FIG. 9A or 10A.

When the saturation voltage V3 is applied between electrodes,substantially no difference exists in refractive index between the bulk38A or 38B and the fine particles 39A or 39B in both oblique and lateraldirections in each of the first and second regions 34A and 34B. Thus,high transparency is obtained in both the regions as shown in FIGS. 9Band 10B.

Case 3

In this case, particle diameter of the fine particles 39B is smallerthan that of the fine particles 39A unlike in the case 1 or 2, so that aliquid crystal in the fine particles 39B hardly moves compared with aliquid crystal in the fine particles 39A. As a result, for example, adrive start voltage V2 of the second region 34B is larger than a drivestart voltage V1 of the first region 34A as shown in FIG. 11. FIG. 11schematically shows a relationship between applied voltage andtransmittance in each of the first and second regions 34A and 34B.

In the case 3, a weight ratio W2 is smaller than the weight ratio W1 asin the case 2, and the weight ratio W2 is larger than that in thecase 1. As a result, for example, the drive start voltage V2 is largerthan the drive start voltage V1, and when no voltage is applied betweenelectrodes, transmittance of the second region 34B is high compared withthat in the case 1 as shown in FIG. 11. That is, in the case 3, thesecond region 34B is substantially transparent during no voltageapplication.

In the case, a drive range defined as a range of a lower limit voltageV_(min) to an upper limit voltage V_(max) is, for example, set as 0(zero) to V3, thereby the second region 34B may be kept to betransparent or substantially transparent while the first region 34A ischanged between a transparent state and a scatterable state. The driverange may be a range other than the above, and, for example, may be V1to V3. Hereinafter, an optical characteristic of each region in the case3 is described.

FIG. 12A schematically shows optical operation of the second region 34Bin the case that no voltage is applied between electrodes. In this case,the bulk 38B is optically isotropic, and thus not aligned. FIG. 12Bschematically shows optical operation of the second region 34B in thecase that a saturation voltage V3 is applied as the upper limit voltageV_(max) between electrodes.

In the case 3, for example, an occupancy rate of the bulk 38B in thesecond region 34B is large compared with that in the case 1, andparticle diameter of the fine particles 39B is small compared with thatin the case 1, as shown in FIGS. 12A and 12B.

In the case 3, an internal configuration of the first region 34A is thesame as that in the case 1. Therefore, when no voltage is appliedbetween electrodes, optical operation of the first region 34A is thesame as optical operation as schematically shown in FIG. 6A. Moreover,when the saturation voltage V3 is applied as the upper limit voltageV_(max) between electrodes, optical operation of the first region 34A isthe same as optical operation as schematically shown in FIG. 6B.

When no voltage is applied between electrodes, for example, a liquidcrystal in the fine particles 39A or 39B is oriented in a randomdirection, and thus not aligned as shown in FIGS. 6A and 12A. That is,the fine particles 39A or 39B are optically isotropic. In contrast, whenthe saturation voltage V3 is applied between electrodes, for example,the liquid crystal in the fine particles 39A or 39B is oriented in thesame or approximately the same direction as a direction of an electricfield E2, and thus aligned in the vertical direction, as shown in FIGS.6B and 12B. That is, the fine particles 39A or 39B are opticallyanisotropic. In such a case, a light axis of the liquid crystal in thefine particles 39A or 39B is oriented in the vertical direction. Thelight axis of the liquid crystal in the fine particles 39A or 39B neednot be necessarily oriented in the vertical direction, and, for example,may be oriented in a direction intersecting with the vertical directiondue to manufacturing errors or the like.

A refractive index of the bulk 38A or 38B is different from a refractiveindex of the fine particles 39A or 39B when the fine particles areoptically isotropic. A refractive index of the bulk 38A is equal to orapproximately equal to an extraordinary index of the fine particles 39Aor 39B when the fine particles are optically anisotropic.

In the first region 34A, when the drive start voltage V1 is appliedbetween electrodes, a difference in refractive index between the bulk38A and the fine particles 39A is large in any direction. As a result,the first region 34A has a high light-scattering ability as shown inFIG. 6A. In contrast, in the second region 34B, for example, anoccupancy rate of the bulk 38B in the second region 34B is largecompared with that in the case 1, and particle diameter of the fineparticles 39B is small compared with that in the case 1 as shown in FIG.12A. Therefore, scattering in the second region 34B is reduced comparedwith that in the case 1, and transmittance of the second region 34B isthus increased compared with that in the case 1. As a result, forexample, the second region 34B becomes substantially transparent despiteoccurrence of slight scattering in the region 34B as shown in FIG. 12A.

When the saturation voltage V3 is applied between electrodes,substantially no difference exists in refractive index between the bulk38A or 38B and the fine particles 39A or 39B in both oblique and lateraldirections in each of the first and second regions 34A and 34B. Thus,high transparency is obtained in both the regions as shown in FIG. 12B.

In any of cases 1, 2 and 3, light L (light in an oblique direction),which is emitted from the light source 20, and propagated through thelight guide plate 10, is, for example, subjected to the followingoperation by the light guide plate 10, the light modulator 30, and thereflector plate 40, and then outputted to the outside. Specifically, thelight L is transmitted through a region (hereinafter, called transparentregion 30A), which becomes transparent by applying the saturationvoltage V3 between electrodes, then reflected (for example, perfectlyreflected) by an interface between the transparent region 30A and air,and then transmitted through the transparent region 30A again andreturned into the light guide plate 10. The light returned into thelight guide plate 10 is reflected (for example, perfectly reflected) bya top of the light guide plate 10, and propagated through the lightguide plate 10. Therefore, luminance of the transparent region 30A isextremely low compared with a case where the light modulator 30 is notprovided (dashed line in FIG. 13B). The light L is scattered within aregion (hereinafter, called scattering region 30B), which haslight-scattering ability by applying the drive start voltage V1 orapplying no voltage between electrodes. A part of the scattered light istransmitted through the light guide plate 10, and then outputted to theoutside. Another part of the scattered light is reflected by thereflector plate 40, then scattered in the scattering region 30B again,or transmitted through the scattering region 30B, and finally outputtedto the outside. Consequently, luminance of the scattering region 30B isextremely high compared with the case where the light modulator 30 isnot provided (dashed line in FIG. 13B), in addition, partialwhite-display luminance (luminance raise) is increased by a levelcorresponding to decrease in luminance of the transparent region 30A.

A refractive index difference (ordinary index minus extraordinary index)of the fine particles 39A is preferably large to the utmost, and ispreferably 0.05 or more, more preferably 0.1 or more, and still morepreferably 0.15 or more. This is because when a difference in refractiveindex of the fine particles 39A is large, the light modulator layer 34has a high light-scattering ability so that a light guide condition maybe easily broken, consequently light is easily extracted from the lightguide plate 10.

For example, the drive circuit 50 controls a voltage applied to the pairof electrodes (the lower electrode 32 and the upper electrode 36) suchthat a light axis of the fine particles 39A or 39B is perpendicular orapproximately perpendicular to a surface of the transparent substrate 31or 37 in one light modulator cell 30A, and a light axis of the fineparticles 39A or 39B shallowly intersects with the surface of thetransparent substrate 31 or 37 in the other light modulator cell 30B.

Hereinafter, a method of manufacturing the backlight 1 of the embodimentis described with reference to FIGS. 14A to 14C to FIGS. 16A to 16C.

First, a transparent conductive film 32A or 36A including ITO is formedon the transparent substrate 31 or 37 including a glass substrate or aplastic film substrate (FIG. 14A). Next, a resist layer is formed overthe whole surface, and then an electrode pattern (a lower electrode 32pattern or an upper electrode 36 pattern) is formed in the resist layerby patterning (FIG. 14B).

A photolithography method or a laser aberration method is preferablyused for the patterning. The electrode pattern is determined dependingon a drive method and dividing number of partial drive. For example,when a 42 inch display is divided into 12*6, a pattern having electrodewidth of about 80 mm is formed, and an inter-electrode slit portion isthinned to the utmost. However, since an excessively thin slit portionis not useful in the light of a gradation characteristic describedlater, specifically, a slit of about 10 to 500 μm is preferably used.Alternatively, the electrode pattern may be formed by printing ITOnanoparticles in a pattern, and then baking the nanoparticles.

Next, an alignment film 33 or 35 is coated over the whole surface, andthen the alignment film is dried and baked (FIG. 14C). When a polyimideseries material is used for the alignment film 33 or 35, NMP(N-methyl-2-pyrolidon) is often used as a solvent. In such a case,temperature of about 200° C. is necessary for the drying and baking inthe air. In this case, when a plastic substrate is used as thetransparent substrate 31 or 37, the alignment film 33 or 35 may be driedand baked in a vacuum at 100° C.

Next, spacers 41 for forming a cell gap are dispersed on the alignmentfilm 33 by a dry or wet process (FIG. 15A). When the light modulatorcell 30A is formed by a vacuum bonding method, spacers 38 may be mixedin a mixture to be dropped. Columnar spacers may be formed by aphotolithography process in place of the spacers 38.

Next, a sealant pattern 42 is coated on the alignment film 35, forexample, in a frame pattern for both bonding and prevention of leakageof a liquid crystal (FIG. 15B). The sealant pattern 42 may be formed bya dispenser method or a screen printing method.

Hereinafter, the vacuum bonding method (One Drop Fill (ODF) method) isdescribed. However, the light modulator cell 30A may be formed even by avacuum injection method or the like.

First, a mixture 43 of a liquid crystal material and a polymerizablematerial, which corresponds to volume determined from a cell gap, cellarea or the like, is uniformly dropped in a plane (FIG. 15C). Alinear-guide precision dispenser is preferably used for dropping themixture 43. However, a die coater may be used with the sealant pattern42 as a bank.

The aforementioned materials may be used as the liquid crystal materialand the polymerizable material respectively, and a weight ratio betweenthe liquid crystal material and the polymerizable material is set to theaforementioned value. While a drive voltage may be reduced by increasinga ratio of the liquid crystal, when the liquid crystal is excessivelyincreased, whiteness is reduced during voltage application, or atransparent state is hardly recovered when voltage application isfinished because response speed is reduced.

The mixture 43 is added with a polymerization initiator in addition tothe liquid crystal material and the polymerizable material. A monomerpercent of a polymerization initiator to be added is adjusted within arange of 0.1 to 10 wt % depending on an ultraviolet wavelength to beused. The mixture 43 may be further added with a polymerizationinhibitor, a plasticizer, or a viscosity modifier if necessary. When thepolymerizable material is a solid or a gel, a base, a syringe, and asubstrate are preferably heated.

The transparent substrates 31 and 37 are disposed in a vacuum bondingmachine (not shown), then the inside of the machine is evacuated, andthe substrates are bonded (FIG. 16A). Then, the bonded substrates arereleased to the air, and a cell gap is made even by uniformpressurization at atmospheric pressure. While the cell gap may beappropriately selected based on a relationship between white luminance(whiteness) and drive voltage, the cell gap is 5 to 40 μm, preferably 6to 20 μm, and more preferably 7 to 10 μm.

After bonding, alignment processing is preferably performed if necessary(not shown). When a bonded cell is inserted between a crossed nicolspolarizer, if light leakage occurs, the cell is heated for a certaintime, or left at room temperature to induce alignment.

Next, a mask M, the open area ratio of which varies depending on adistance from a region where the light source 20 is to be disposed, isdisposed on the transparent substrate 37 (FIG. 16B). The open area ratioof the mask M is increased with increase in distance from the regionwhere the light source 20 is to be disposed. Next, light L₃ (forexample, ultraviolet rays) is strongly irradiated to the polymerizablematerial in the mixture 43 via the mask M (FIG. 16B). Thus, thepolymerizable material is polymerized into a polymer in areas stronglyirradiated with light, specifically, in areas of the mixture 43corresponding to openings (not shown) formed in the mask M, and besides,the liquid crystal material and the polymerizable material arephase-separated from each other. As a result, the first region 34A (notshown) is formed in the areas strongly irradiated with light. Anoccupancy rate of the first region 34A in the mixture 43 is increasedwith increase in distance from the region where the light source 20 isto be disposed.

Polymerization and phase separation concurrently proceed in the processwhere the liquid crystal material and the polymerizable material areirradiated with ultraviolet rays. Since polymerization speed is fasterthan phase separation speed of a liquid crystal with increase inultraviolet illuminance, liquid crystal droplets with small diametertend to be formed. Since the mixture 43 is of a normally white type, asilluminance increases, scattering ability of the mixture tends to beincreased, and a drive start voltage tends to be increased. Therefore,the above light irradiation process increases scattering ability of thefirst region 34A, and decreases scattering ability of other regions,leading to improvement in transparency.

Next, light is weakly irradiated to areas where the second region 34B isto be formed. For example, weak light L₄ is irradiated to the mixture 43as a whole without using the mask M as shown in FIG. 16C. Thus, thepolymerizable material is polymerized into a polymer, and besides, theliquid crystal material and the polymerizable material arephase-separated from each other in the areas where the second region 34Bis to be formed. As a result, the second region 34B (not shown) isformed in areas other than the first region 34A of the mixture 43.

In this way, in the embodiment, the first region 34A and the secondregion 34B are formed in accordance with intensity of irradiated lightand a mask pattern. Moreover, the mask M varies in open area ratiodepending on a distance from the region where the light source 20 is tobe disposed. Therefore, an occupancy rate of the first region 34A in themixture 43 may be varied depending on the distance from the region wherethe light source 20 is to be disposed. In this way, in the embodiment,each of the first region 34A and the second region 34B may be formed inthe mixture 43 with an occupancy rate depending on the distance from theregion where the light source 20 is to be disposed by a simple method oflight irradiation using the mask M. In this way, the light modulator 30is manufactured.

In the manufacturing method, a mask, the open area ratio of which varieswith increase in distance from the region where the light source 20 isto be disposed, is used as the mask M. However, another mask may be usedinstead of the mask having transmissive portions and shading portionsdiscontinuous to each other. For example, a gray mask may be used as themask M, the gray mask having a transmittance being gradually increasedwith increase in distance from the region where the light source 20 isto be disposed. In the manufacturing steps, cell temperature ispreferably not changed during ultraviolet irradiation. In addition, thecell temperature is preferably kept high during the irradiation. In sucha case, transparency of the second region 34B may be increased.Moreover, an infrared cut filter is preferably used, or UV-LED ispreferably used for the light source. Moreover, since ultraviolet raysaffect a structure of a composite material, illuminance of ultravioletrays is preferably appropriately adjusted based on a liquid crystalmaterial or a monomer material to be used, or a composition of thematerials.

When droplet diameter of a liquid crystal in the fine particles 39A isdesired to be different from that in the fine particles 39B, a processexemplified below is preferably used. For example, a seal pattern isdrawn, then materials, which are different in weight ratio between aliquid crystal and a polymerizable material, may be separately coated(patterned) on areas corresponding to the first region 34A and to thesecond region 34B by using a dispenser method, a screen printing method,an inkjet method or the like. Alternatively, a process may be used,where only the polymerizable material (for example, acrylic ultravioletcuring resin) is coated on an area corresponding to the second region34B, then a material to be used is dropped onto the first region 34A. Inthe case of using the latter process, ultraviolet rays are collectivelyirradiated to the whole surface with the same irradiation, so that thefirst region 34A and the second region 34B, the regions being differentin transparency from each other, may be formed. Moreover, an areairradiated with high ultraviolet illuminance and an area irradiated withlow ultraviolet illuminance may be formed by using a mask as describedbefore.

Then, the light modulator 30 is bonded to the light guide plate 10.While the light modulator may be bonded by either of sticking andadhesion, the light modulator is preferably bonded by using a materialhaving a refractive index being close to a refractive index of the lightguide plate 10 and to a refractive index of a substrate material of thelight modulator 30 to the utmost. Finally, lead lines (not shown) areattached to the lower and upper electrodes 32 and 36 respectively. Inthis way, the backlight 1 of the embodiment is manufactured.

Description has been made on such a process that the light modulator 30is formed, and finally the light modulator 30 is bonded to the lightguide plate 10. However, a transparent substrate 37 having the alignmentfilm 35 formed thereon may be beforehand bonded to a surface of thelight guide plate 10 to form the backlight 1. The backlight 1 may beformed by either of a sheet-feed method and a roll-to-roll method.

Next, operation and effects of the backlight 1 of the embodiment aredescribed.

In the backlight 1 of the embodiment, the light modulator 30 adhered tothe light guide plate 10 includes the first region 34A being changedbetween the transparent state and the scatterable state depending onintensity of an electric field, and the second region 34B being moretransparent than the first region 34A in a scatterable state at anelectric field having certain intensity, the electric field beingapplied when the first region 34A is changed between the states. Thus,light from the light source 20 is incident to the light guide plate 10,and perfectly reflected or reflected with a high reflectance by a top ofthe light guide plate 10, or by a bottom of a region (transparent region30A), which becomes transparent by controlling an electric field, of thelight modulator layer 34, and propagated through the light guide plate10 and the light modulator 30 (refer to FIG. 13). This decreasesluminance of an area corresponding to the transparent region 30A in alight emitting area of the backlight 1. In contrast, the lightpropagated through the light guide plate 10 and the light modulator 30is scattered by a region (scattering region 30B), which haslight-scattering ability by controlling an electric field, of the lightmodulator layer 34. A part of the scattered light, which is transmittedthrough a bottom of the scattering region 30B, is reflected by thereflector plate 40, and returned to the light guide plate 10, and thenoutputted from a top of the backlight 1. Another part of the scatteredlight, which is directed to a top of the scattering region 30B, istransmitted through the light guide plate 10, and then outputted fromthe top of the backlight 1.

In this way, in the embodiment, light is hardly outputted from the topof the transparent region 30A, and largely outputted from the top of thescattering region 30B. This increases luminance of an area correspondingto the scattering region 30B in the light emitting area of the backlight1. As a result, a modulation ratio in a front direction is increased.

In the embodiment, for example, luminance of the transparent region 30A(luminance of black display) is low compared with a case where the lightmodulator 30 is not provided (dashed line in FIG. 13B) as shown in FIGS.13A and 13B. On the other hand, luminance of the scattering region 30Bis high compared with the case where the light modulator 30 is notprovided (dashed line in FIG. 13B), in addition, partial white-displayluminance (luminance raise) is increased by a level corresponding todecrease in luminance of the transparent region 30A.

The luminance raise is a technique of increasing luminance in a casewhere white display is partially performed compared with a case wherewhite display is wholly performed. The technique is generally used inCRT or PDP. However, in a liquid crystal display, since a backlightuniformly emits light all over the screen regardless of an image,luminance may not be partially increased. In the case of using an LEDbacklight where a plurality of LED are two-dimensionally arranged, theLED may be partially turned off. However, in such a case, since diffusedlight from a dark area where the LED are turned off is lost, luminanceis reduced compared with a case where all LED are turned on. Luminancemay be increased by increasing current flowing to LED being partiallyturned on. However, in such a case, a large current flows in anextremely short time, leading to a difficulty in circuit load orreliability.

In contrast, in the embodiment, when a refractive index of the bulks 38Aor 38B is equal to or approximately equal to an ordinary index of thefine particles 39A or 39B, scattering in a front direction issuppressed, so that leakage light from the light guide plate is reducedin a dark state. Thus, since light is guided from a partially darkportion to a partially bright portion, luminance raise may be achievedwithout increasing input power to the backlight 1.

In the embodiment, an occupancy rate of the first region 34A in thelight modulator layer 34 is increased with increase in distance from thelight source 20. Thus, luminance of a light source 20 side of a lightemitting area of the backlight 1 may be controlled low compared with acase where the light modulator 30 is not provided, and luminance on aside opposite to the light source 20 side of the light emitting area maybe increased compared with the case where the light modulator 30 is notprovided. As a result, luminance may be made uniform in a plane not onlyin a case where the whole light emitting area of the backlight 1 isdarkened, for example, as shown in FIG. 17B, but also in a case wherethe whole light emitting area of the backlight 1 is lightened, forexample, as shown in FIG. 17C. Consequently, for example, when whitedisplay is performed in an area α₁ near the light source 20 and in anarea α₂ away from the light source 20, white luminance may be equalizedbetween both the areas as shown in FIG. 17D. Moreover, for example, whenblack display is performed in an area β₁ near the light source 20compared with the area α₁, in an area β₂ between the area α₁ and thearea α₂, and in area β₃ away from the light source 20 compared with thearea α₂, black luminance may be equalized between the areas as shown inFIG. 17D.

Modification

In the embodiment, the light modulator 30 is adherently bonded to theback (bottom) of the light guide plate 10 without inserting an airlayer. However, for example, the light modulator 30 may be adherentlybonded to the top of the light guide plate 10 without inserting an airlayer as shown in FIG. 18. Alternatively, for example, the lightmodulator 30 may be provided within the light guide plate 10 as shown inFIG. 19. However, even in this case, the light modulator 30 needs to beadherently bonded to the light guide plate 10 without inserting an airlayer.

While a component is not particularly provided on the light guide plate10 in the embodiment, for example, an optical sheet 70 (for example, adiffuser plate, a diffuser sheet, a lens film, or a polarizationseparation sheet) may be provided on the light guide plate 10 as shownin FIG. 20.

Second Embodiment

FIG. 21A shows an example of a sectional configuration of a backlight 2(illumination device) according to a second embodiment of the invention.FIG. 21B shows an example of a sectional configuration of a lightmodulator 60 (described later) incorporated in the backlight 2 of FIG.21A. FIGS. 21A and 21B schematically show the examples, and therefore adimension or shape is not limited to be the same as an actual dimensionor shape in the figures. The backlight 2, for example, illuminates aliquid crystal display panel from a back of the panel as the backlight 1of the first embodiment and the modification, but different from theconfiguration of the backlight 1 in that the light modulator 60 isprovided in place of the light modulator 30. Thus, hereinafter,different points from the first embodiment and the modification aremainly described, and description of points in common with the firstembodiment and the modification is appropriately omitted.

The light modulator 60 is, for example, formed by disposing atransparent substrate 31, a lower electrode 32, an alignment film 33, alight modulator layer 64, an alignment film 35, an upper electrode 36and a transparent substrate 37 in order from a side of the reflectorplate 40 as shown in FIG. 21B.

The light modulator layer 64 has, for example, two regions (first region64A and second region 64B) different in optical characteristic at acertain electric-field intensity as shown in FIG. 21B. The first region64A and the second region 64B have, for example, a columnar shapeextending in a stacking direction of the light modulator 60respectively. The first region 64A is formed filling the periphery ofthe second region 64B, and the second region 64B is dispersed within thefirst region 64A as viewed from a top of the light modulator layer 64.

The second region 64B has, for example, a cylindrical shape, anelliptical cylinder shape, or a prismatic shape. For example, diameterof the second region 64B is constant regardless of a distance from thelight source 20, and for example, about several micrometers to severalmillimeters. The diameter of the second region 64B need not benecessarily constant, and, for example, may be decreased with increasein distance from the light source 20. When the diameter of the secondregion 64B is constant, an occupancy rate (density) of the second region64B in the light modulator layer 64 is, for example, decreased withincrease in distance from the light source 20. When the diameter of thesecond region 64B is decreased with increase in distance from the lightsource 20, number of the second region 64B per area is set such that anoccupancy rate (density) of the region 64B in the light modulator layer64 is decreased with increase in distance from the light source 20.Consequently, in each case, an occupancy rate of the first region 64A inthe light modulator layer 64 is constant in a thickness direction, andincreased with increase in distance from the light source 20 in anin-plane direction.

The first region 64A and the second region 64B need not necessarily havea columnar shape. For example, when the first region 64A has a bulkshape, and the second region 64B has a block shape, the light modulatorlayer 64 may be configured such that the second region 64B is dispersedin the first region 64A not only in an in-plane direction but also in athickness direction. When the second region 64B is uniformly dispersedin the thickness direction, and dispersed more thinly with increase indistance from the light source 20 in an in-plane direction, an occupancyrate of the first region 64A in the light modulator layer 64 is constantin a thickness direction, and increased with increase in distance fromthe light source 20 in an in-plane direction. When the second region 64Bis nonuniformly dispersed in the thickness direction, and dispersed morethinly with increase in distance from the light source 20 in an in-planedirection, an occupancy rate of the first region 64A in the lightmodulator layer 64 varies in a thickness direction, and is increasedwith increase in distance from the light source 20 in an in-planedirection.

The first region 64A includes, for example, a bulk 68A (third region)and fine particles 69A (fourth region). The second region 64B includes,for example, a bulk 68B (fifth region) and fine particles 69B (sixthregion). The bulk 68A is different in response speed to an electricfield from the fine particles 69A. The bulk 68A or 68B has, for example,a streaky or porous structure nonrespondent to an electric field, or hasa rodlike structure having a response speed lower than that of the fineparticles 69A or 69B. The bulk 68A or 68B is, for example, formed bypolymerizing a material having an aligning property and a polymerizingproperty (for example, monomer), which is aligned along an alignmentdirection of the fine particles 69A or 69B or an alignment direction ofthe bulk 68A or 68B, by at least one of heat and light. In contrast, thefine particles 69A or 69B, for example, mainly include a liquid crystalmaterial, and have a sufficiently fast response speed compared withresponse speed of the bulk 68A or 68B.

While the monomer having aligning and polymerizing properties may be amaterial that is optically anisotropic, and may be combined with aliquid crystal, the monomer is preferably a low molecular monomer to becured by ultraviolet rays in the embodiment. Since it is preferable thatoptically anisotropic directions of the liquid crystal corresponds tothat of a polymerized product of the low molecular monomer (high-polymermaterial) during no voltage application, the liquid crystal and the lowmolecular monomer are preferably aligned in the same direction beforeultraviolet curing. When a liquid crystal is used for the fine particles69A, in the case that the liquid crystal includes rodlike molecules,even a monomer material to be used preferably has a rodlike shape. Fromthe above, a material having both of a polymerizing property and aliquid-crystal property is preferably used as the monomer material, and,for example, the material preferably has at least one functional groupselected from groups including an acryloyloxy group, a methacryloyloxygroup, a vinyl ether group, and an epoxy group as a polymerizablefunctional group. The functional groups may be polymerized byirradiating ultraviolet rays, infrared rays or an electron beam, or byheating. A liquid crystal material having a multifunctional group may beadded to suppress reduction in alignment during ultraviolet irradiation.

A weight ratio W3 between the fine particles 69A and the bulk 68A(weight of the fine particles 69A/weight of the bulk 68A) is differentfrom a weight ratio W4 between the fine particles 69B and the bulk 68B(weight of the fine particles 69B/weight of the bulk 68B). Specifically,the weight ratio W4 is smaller than the weight ratio W3. The weightratio W3 is, for example, 95/5 to 65/35, and the weight ratio W4 is, forexample, 5/95 to 35/65. When the weight ratio W4 is within theexemplified range, the second region 64B may act as spacers for keepinga cell gap.

In the embodiment, both the first and second regions 64A and 64B areconfigured such that an optical axis of each of the fine particles 69Aand 69B, for example, becomes perpendicular to a surface parallel to asurface of each of the transparent substrates 31 and 37, or becomesparallel to the surface. Thus, each of the first and second regions 64Aand 64B may be changed between a transparent state and a scatterablestate as described later. However, voltage for changing the first region64A between the transparent state and the scatterable state and voltagefor changing the second region 64B between the states are different fromeach other depending on a magnitude relationship between the weightratios W3 and W4.

Hereinafter, an optical characteristic of each of the first and secondregions 64A and 64B is described in detail while being classified intothree cases. The classification is made focusing on three factors of (1)size of particle diameter of the fine particles 69B, (2) magnituderelationship between the weight ratios W3 and W4, and (3) an occupancyrate of the fine particles 69B in the second region 64B.

Case 1

In this case, particle diameter of the fine particles 69B is smallerthan that of the fine particles 69A, so that a liquid crystal in thefine particles 69B hardly moves compared with a liquid crystal in thefine particles 69A. As a result, for example, a drive start voltage V6of the second region 64B is higher than a drive start voltage V5 of thefirst region 64A, and a saturation voltage V8 of the second region 64Bis larger than a saturation voltage V7 of the first region 64A, as shownin FIG. 22. FIG. 22 schematically shows a relationship between appliedvoltage and transmittance in each of the first and second regions 64Aand 64B.

In the case 1, particle diameter of the fine particles 69B is smallerthan that of the fine particles 69A, and besides, the weight ratio W4 issmaller than the weight ratio W3. Therefore, the second region 64B has alow light-scattering ability during voltage application. As a result, asshown in FIG. 22, when the saturation voltage V7 is applied betweenelectrodes, transmittance of the second region 64B is somewhat high, andthe second region 64B is thus substantially transparent. In the case 1,a drive range defined as a range of a lower limit voltage V_(min) to anupper limit voltage V_(max) is, for example, set as 0 (zero) to V7,thereby the second region 64B may be kept to be transparent orsubstantially transparent while the first region 64A is changed betweena transparent state and a scatterable state. The drive range may be arange other than the above, and, for example, may be 0 (zero) to V6, V5to V7, or V5 to V6. Hereinafter, the optical characteristic of eachregion in the case 1 is described.

FIG. 23A schematically shows optical operation of the first region 64Ain the case that 0 (zero) volt is applied as the lower limit voltageV_(min) between electrodes (no voltage is applied between electrodes).In this case, the bulk 68A is optically anisotropic, and is aligned inthe vertical direction. FIG. 23B schematically shows optical operationof the first region 64A in the case that the saturation voltage V7 ofthe first region 64A is applied as the upper limit voltage V_(max)between electrodes. FIG. 24A schematically shows optical operation ofthe second region 64B in the case that 0 (zero) volt is applied as thelower limit voltage V_(min) between electrodes. In this case, the bulk68B is optically isotropic, and is not aligned. FIG. 24B schematicallyshows optical operation of the second region 64B in the case that thesaturation voltage V7 is applied as the upper limit voltage V_(max)between electrodes.

When no voltage is applied between electrodes, for example, a liquidcrystal in the fine particles 69A or 69B is oriented in the verticaldirection, and thus aligned in the vertical direction as shown in FIGS.23A and 24A. That is, the fine particles 69A or 69B are opticallyanisotropic. At that time, a light axis of the liquid crystal in thefine particles 69A or 69B is oriented in the vertical direction, andoriented in the same direction as a direction of a light axis of thebulk 68A or 68B. That is, the direction of the light axis of the liquidcrystal in the fine particles 69A or 69B corresponds (is parallel) tothe direction of the light axis of the bulk 68A or 68B. The light axisof the liquid crystal in the fine particles 69A or 69B or the light axisof the bulk 68A or 68B need not be necessarily oriented in the verticaldirection, and may be oriented in a direction intersecting with thevertical direction due to manufacturing errors or the like. In contrast,when the saturation voltage V7 is applied between electrodes, forexample, the liquid crystal in the fine particles 69A or 69B is orientedin a random direction regardless of a direction of an electric field E3,and thus not aligned as shown in FIGS. 23B and 24B. That is, the fineparticles 69A or 69B are optically isotropic.

A refractive index of the bulk 68A or 68B is different from a refractiveindex of the fine particles 69A or 69B when the fine particles areoptically isotropic. Ordinary and extraordinary indexes of the bulk 68Aare equal to or approximately equal to ordinary and extraordinaryindexes of the fine particles 69A or 69B when the fine particles areoptically anisotropic.

In the first region 64A, when the saturation voltage V7 is appliedbetween electrodes, a difference in refractive index between the bulk68A and the fine particles 69A is large in any direction. As a result,the first region 64A has a high light-scattering ability as shown inFIG. 23B. In contrast, in the second region 64B, for example, particlediameter of the fine particles 69B is smaller than particle diameter ofthe fine particles 69A as shown in FIG. 24B, so that the liquid crystalin the fine particles 69B hardly moves compared with the liquid crystalin the fine particles 69A. Thus, an orientation of the liquid crystal,which has been oriented in a random direction in the fine particles 69B,is substantially not changed, and thus substantially no differenceexists in refractive index between the bulk 68B and the fine particles69B in any direction. As a result, the second region 64B becomestransparent or substantially transparent as shown in FIG. 24B.

When no voltage is applied between electrodes, substantially nodifference exists in refractive index between the bulks 68A or 68B andthe fine particles 69A or 69B in any direction in each of the firstregion 64A and the second region 64B. Thus, high transparency isobtained in both the regions as shown in FIGS. 23A and 24A.

Case 2

In this case, particle diameter of the fine particles 69B is smallerthan that of the fine particles 69A as in the case 1. As a result, forexample, a drive start voltage V6 of the second region 64B is higherthan a drive start voltage V5 of the first region 64A, and a saturationvoltage V8 of the second region 64B is higher than a saturation voltageV7 of the first region 64A as shown in FIG. 25. FIG. 25 schematicallyshows a relationship between applied voltage and transmittance in eachof the first and second regions 64A and 64B.

Furthermore, in the case 2, the weight ratio W4 is smaller than theweight ratio W3 as in the case 1, but the weight ratio W4 is smallerthan that in the case 1. As a result, for example, the drive startvoltage V6 is larger than the drive start voltage V5, and when thesaturation voltage V8 is applied between electrodes, transmittance ofthe second region 64B is high compared with transmittance of the secondregion 64B during application of the saturation voltage V8 in the case 1as shown in FIG. 25.

In the case 2, a drive range defined as a range of a lower limit voltageV_(min), to an upper limit voltage V_(max) is, for example, set as 0(zero) to V7, thereby the second region 64B may be kept to betransparent or substantially transparent while the first region 64A ischanged between a transparent state and a scatterable state. The driverange may be a range other than the above, and, for example, may be 0(zero) to V6, V5 to V7, or V5 to V6. Hereinafter, an opticalcharacteristic of each region in the case 2 is described.

FIGS. 26A and 27A schematically show optical operation of the secondregion 64B in the case that no voltage is applied between electrodes. Inthis case, the bulk 68B is optically anisotropic, and thus aligned inthe vertical direction. FIGS. 26B and 27B schematically show opticaloperation of the second region 64B in the case that the saturationvoltage V7 is applied as the upper limit voltage V_(max) betweenelectrodes.

In the case 2, for example, an occupancy rate of the bulk 68B in thesecond region 64B is large compared with that in the case 1 as shown inFIGS. 26A and 26B, or, for example, particle diameter of the fineparticles 69B is extremely small compared with that in the case 1 asshown in FIGS. 27A and 27B.

In the case 2, an internal configuration of the first region 64A is thesame as that in the case 1. Therefore, when no voltage is appliedbetween electrodes, optical operation of the first region 64A is thesame as optical operation as schematically shown in FIG. 23A. Moreover,when the saturation voltage V7 is applied as the upper limit voltageV_(max) between electrodes, optical operation of the first region 64A isthe same as optical operation as schematically shown in FIG. 23B.

When no voltage is applied between electrodes, for example, a liquidcrystal in the fine particles 69A or 69B is oriented in the verticaldirection, and thus aligned in the vertical direction as shown in FIGS.23A and 26A or FIG. 27A. That is, the fine particles 69A or 69B areoptically anisotropic. At that time, a light axis of a liquid crystal inthe fine particles 69A or 69B is oriented in the vertical direction, andoriented in the same direction as a direction of a light axis of thebulk 68A or 68B. That is, the direction of the light axis of the liquidcrystal in the fine particles 69A or 69B corresponds (is parallel) tothe direction of the light axis of the bulk 68A or 68B. The light axisof the liquid crystal in the fine particles 69A or 69B or the light axisof the bulk 68A or 68B need not be necessarily oriented in the verticaldirection, and may be oriented in a direction intersecting with thevertical direction, for example, due to manufacturing errors or thelike. In contrast, when the saturation voltage V7 is applied betweenelectrodes, for example, the liquid crystal in the fine particles 69Aand 69B is oriented in a random direction regardless of a direction ofan electric field E3, and thus not aligned as shown in FIGS. 23B and 26Bor FIG. 27B. That is, the fine particles 69A or 69B are opticallyisotropic.

A refractive index of the bulk 68A or 68B is different from a refractiveindex of the fine particles 69A or 69B when the fine particles areoptically isotropic. A refractive index of the bulk 68A is equal to orapproximately equal to an extraordinary index of the fine particles 69Aor 69B when the fine particles are optically anisotropic.

In the first region 64A, when the saturation V7 is applied betweenelectrodes, a difference in refractive index between the bulk 68A andthe fine particles 69A is large in any direction. As a result, the firstregion 64A has a high light-scattering ability as shown in FIG. 23B. Incontrast, in the second region 64B, for example, particle diameter ofthe fine particles 69B is smaller than particle diameter of the fineparticles 69A as shown in FIG. 26B or 27B. Furthermore, an occupancyrate of the bulk 68B in the second region 64B is large compared withthat in the case 1, or particle diameter of the fine particles 69B isextremely small compared with that in the case 1. Therefore, scatteringin the second region 64B is reduced compared with that in the case 1, ordoes not occur at all, and transmittance of the second region 64B isthus high compared with that in the case 1. As a result, for example,the second region 64B becomes transparent or substantially transparentas shown in FIG. 26B or 27B.

When no voltage is applied between electrodes, substantially nodifference exists in refractive index between the bulk 68A or 68B andthe fine particles 69A or 69B in any direction in each of the first andsecond regions 64A and 64B. Thus, high transparency is obtained in boththe regions as shown in FIGS. 26A and 27A.

Case 3

In this case, particle diameter of the fine particles 69B is larger thanthat of the fine particles 69A unlike in the case 1 or 2, so that aliquid crystal in the fine particles 69B easily moves compared with aliquid crystal in the fine particles 69A. As a result, for example, adrive start voltage V6 of the second region 64B is smaller than a drivestart voltage V5 of the first region 64A as shown in FIG. 28. FIG. 28schematically shows a relationship between applied voltage andtransmittance in each of the first and second regions 64A and 64B.

In the case 3, a weight ratio W4 is smaller than the weight ratio W3 asin the case 2, and the weight ratio W4 is smaller than that in thecase 1. As a result, for example, the drive start voltage V6 is smallerthan the drive start voltage V5 as shown in FIG. 28, and when asaturation voltage V8 is applied between electrodes, transmittance ofthe second region 64B is high compared with that in the case 1. That is,in the case 3, the second region 64B is substantially transparent duringapplying the saturation voltage V7.

In the case 3, a drive range defined as a range of a lower limit voltageV_(min), to an upper limit voltage V_(max) is, for example, set as 0(zero) to V7, thereby the second region 64B may be kept to betransparent or substantially transparent while the first region 64A ischanged between a transparent state and a scatterable state. The driverange may be a range other than the above, and, for example, may be 0(zero) to V6, V5 to V7, or V5 to V6. Hereinafter, an opticalcharacteristic of each region in the case 3 is described.

FIGS. 29A and 30A schematically show optical operation of the secondregion 64B in the case that no voltage is applied between electrodes. Inthis case, the bulk 68B is optically anisotropic, and thus aligned inthe vertical direction. FIGS. 29B and 30B schematically show opticaloperation of the second region 64B in the case that a saturation voltageV7 is applied as the upper limit voltage V_(max) between electrodes.

In the case 3, for example, an occupancy rate of the bulk 68B in thesecond region 64B is large compared with that in the case 1 as shown inFIGS. 29A and 29B, or, for example, particle diameter of the fineparticles 69B is extremely large compared with that in the case 1 asshown in FIGS. 30A and 30B.

In the case 3, an internal configuration of the first region 64A is thesame as that in the case 1. Therefore, when no voltage is appliedbetween electrodes, optical operation of the first region 64A is thesame as optical operation as schematically shown in FIG. 23A. Moreover,when the saturation voltage V7 is applied as the upper limit voltageV_(max) between electrodes, optical operation of the first region 64A isthe same as optical operation as schematically shown in FIG. 23B.

When no voltage is applied between electrodes, for example, liquidcrystal in the fine particles 69A or 69B is oriented in the verticaldirection, and thus aligned in the direction as shown in FIGS. 23A and29A or FIG. 30B. That is, the fine particles 69A or 69B are opticallyanisotropic. At that time, a light axis of a liquid crystal in the fineparticles 69A or 69B is oriented in the vertical direction, and orientedin the same direction as a direction of a light axis of the bulk 68A or68B. That is, the direction of the light axis of the liquid crystal inthe fine particles 69A or 69B corresponds (is parallel) to the directionof the light axis of the bulk 68A or 68B. The light axis of the liquidcrystal in the fine particles 69A or 69B or the light axis of the bulk68A or 68B need not be necessarily oriented in the vertical direction,and may be oriented in a direction intersecting with the verticaldirection, for example, due to manufacturing errors or the like. Incontrast, when the saturation voltage V7 is applied between electrodes,for example, the liquid crystal in the fine particles 69A or 69B isoriented in a random direction regardless of a direction of an electricfield E3, and thus not aligned as shown in FIGS. 23B and 29B or FIG.30B. That is, the fine particles 69A or 69B are optically isotropic.

A refractive index of the bulk 68A or 68B is different from a refractiveindex of the fine particles 69A or 69B when the fine particles areoptically isotropic. Ordinary and extraordinary indexes of the bulk 68Aare equal to or approximately equal to ordinary and extraordinaryindexes of the fine particles 69A or 69B when the fine particles areoptically anisotropic.

In the first region 64A, when the drive start voltage V7 is appliedbetween electrodes, a difference in refractive index between the bulk68A and the fine particles 69A is large in any direction. As a result,the first region 64A has a high light-scattering ability as shown inFIG. 23B. In contrast, in the second region 64B, for example, anoccupancy rate of the bulk 68B in the second region 64B is largecompared with that in the case 1 as shown in FIG. 29B, or, for example,particle diameter of the fine particles 69B is extremely large comparedwith that in the case 1 as shown in FIG. 30B. Therefore, scattering inthe second region 64B is reduced compared with that in the case 1, andtransmittance of the second region 64B is thus increased compared withthat in the case 1. As a result, for example, the second region 64Bbecomes substantially transparent despite slight occurrence ofscattering in the region 64B as shown in FIG. 29B or 30B.

When no voltage is applied between electrodes, substantially nodifference exists in refractive index between the bulk 68A or 68B andthe fine particles 69A or 69B in any direction in each of the first andsecond regions 64A and 64B. Thus, high transparency is obtained in boththe regions as shown in FIG. 29A or 30A.

In any of cases 1, 2 and 3, light L (light in an oblique direction),which is emitted from the light source 20, and propagated through thelight guide plate 10, is, for example, subjected to the followingoperation by the light guide plate 10, the light modulator 30, and thereflector plate 40, and then outputted to the outside. Specifically, thelight L is transmitted through a region (hereinafter, called transparentregion 30A) that becomes transparent by applying no voltage betweenelectrodes, then reflected (for example, perfectly reflected) by aninterface between the transparent region 30A and air, and thentransmitted through the transparent region 30A again and returned intothe light guide plate 10. The light returned into the light guide plate10 is reflected (for example, perfectly reflected) by a top of the lightguide plate 10, and propagated through the light guide plate 10.Therefore, luminance of the transparent region 30A is extremely lowcompared with a case where the light modulator 30 is not provided(dashed line in FIG. 13B). The light L is scattered within a region(hereinafter, called scattering region 30B), which has light-scatteringability by applying the saturation voltage V7 between electrodes. A partof the scattered light is transmitted through the light guide plate 10,and then outputted to the outside. Another part of the scattered lightis reflected by the reflector plate 40, then scattered in the scatteringregion 30B again, or transmitted through the scattering region 30B, andfinally outputted to the outside. Consequently, luminance of thescattering region 30B is extremely high compared with the case where thelight modulator 30 is not provided (dashed line in FIG. 13B), inaddition, partial white-display luminance (luminance raise) is increasedby a level corresponding to decrease in luminance of the transparentregion 30A.

The ordinary index of the bulk 68A may be somewhat different from theordinary index of the fine particles 69A due to manufacturing errors orthe like, and such a difference is, for example, preferably 0.1 or less,and more preferably 0.05 or less. Similarly, the extraordinary index ofthe bulk 68A may be somewhat different from the extraordinary index ofthe fine particles 69A due to manufacturing errors or the like, and sucha difference is, for example, preferably 0.1 or less, and morepreferably 0.05 or less.

A refractive index difference (Δn, ordinary index minus extraordinaryindex) of the bulk 68A, or a refractive index difference (Δn, ordinaryindex minus extraordinary index) of the fine particles 69A is preferablylarge to the utmost, and is preferably 0.05 or more, more preferably 0.1or more, and still more preferably 0.15 or more. This is because when arefractive index difference of each of the bulk 68A and the fineparticles 69A is large, the light modulator layer 64 has a highlight-scattering ability, so that a light guide condition may be easilybroken, consequently light is easily extracted from the light guideplate 10.

Hereinafter, a method of manufacturing the backlight 2 of the embodimentis described. Since the manufacturing method of the embodiment is thesame as the manufacturing method of the first embodiment up to a step ofdisposing the mask M on the transparent substrate 37, subsequent stepsare described.

The mask M is disposed on the transparent substrate 37, then light (forexample, ultraviolet rays) is irradiated to the exemplified mixture 43including the liquid crystal material and the polymerizable material viathe mask M, the light being weakly irradiated compared with in the caseof the first embodiment. Thus, the polymerizable material is polymerizedinto a polymer in areas weakly irradiated with light, specifically, inareas of the mixture 43 corresponding to openings (not shown) formed inthe mask M, in addition, the liquid crystal material and thepolymerizable material are phase-separated from each other. As a result,the first region 64A (not shown) is formed in the areas weaklyirradiated with light. An occupancy rate of the first region 64A in themixture 43 is increased with increase in distance from a region wherethe light source 20 is to be disposed.

Next, light is strongly irradiated to areas where the second region 64Bis to be formed. For example, a component having a pattern reverse to apattern of the mask M is disposed on the transparent substrate 37, andthen strong light is irradiated to the relevant areas with the componentas a mask. Thus, the polymerizable material is polymerized into apolymer, in addition, the liquid crystal material and the polymerizablematerial are phase-separated from each other in the areas where thesecond region 64B is to be formed. As a result, the second region 64B(not shown) is formed in areas of the mixture 43 other than the firstregions 64A.

In this way, in the embodiment, the first region 64A and the secondregion 64B are formed in accordance with intensity of irradiated lightand a mask pattern. Moreover, the mask M varies in open area ratiodepending on a distance from the region where the light source 20 is tobe disposed. Therefore, an occupancy rate of the first region 64A in themixture 43 may be varied depending on the distance from the region wherethe light source 20 is to be disposed. In this way, in the embodiment,each of the first region 64A and the second region 64B may be formed inthe mixture 43 with an occupancy rate depending on the distance from theregion where the light source 20 is to be disposed by using lightirradiation using the mask M. In this way, the light modulator 60 ismanufactured.

In the manufacturing method, a mask, the open area ratio of whichincreases with increase in distance from the region where the lightsource 20 is to be disposed, is used as the mask M. However, anothermask may be used instead of the mask having transmissive portions andshading portions discontinuous to each other as in the first embodiment.In the manufacturing steps, cell temperature is preferably not changedduring ultraviolet irradiation. In addition, the cell temperature ispreferably kept high during that. In such a case, transparency of thesecond region 64B may be increased. Moreover, an infrared cut filter ispreferably used, or UV-LED is preferably used for the light source.Moreover, since ultraviolet rays affect a structure of a compositematerial, illuminance of ultraviolet rays is preferably appropriatelyadjusted based on a liquid crystal material or a monomer material to beused, or a composition of the materials.

When droplet diameter of a liquid crystal in the fine particles 69A isdesired to be different from that in the fine particles 69B, the sameprocess as exemplified in the first embodiment is preferably used.

Then, the light modulator 60 is bonded to the light guide plate 10, andthen lead lines (not shown) are attached to the lower and upperelectrodes 32 and 36 respectively. In this way, the backlight 2 of theembodiment is manufactured.

Description has been made on such a process that the light modulator 60is formed, and finally the light modulator 60 is bonded to the lightguide plate 10. However, a transparent substrate 37 having the alignmentfilm 35 formed thereon may be beforehand bonded to a surface of thelight guide plate 10 to form the backlight 2. Moreover, the backlight 2may be formed by either of a sheet-feed method and a roll-to-rollmethod.

Next, operation and effects of the backlight 2 of the embodiment aredescribed.

In the backlight 2 of the embodiment, light from the light source 20 isincident to the light guide plate 10, and perfectly reflected orreflected with a high reflectance by a top of the light guide plate 10,or by a bottom of a region (transparent region 30A), which becomestransparent by controlling an electric field, of the light modulatorlayer 64, and propagated through the light guide plate 10 and the lightmodulator 60. This decreases luminance of an area corresponding to thetransparent region 30A in a light emitting area of the backlight 2. Incontrast, light propagated through the light guide plate 10 and thelight modulator 60 is scattered by a region (scattering region 30B),which has light-scattering ability by controlling an electric field, ofthe light modulator layer 64. A part of the scattered light, which istransmitted through the bottom of the scattering region 30B, isreflected by the reflector plate 40, and returned to the light guideplate 10, and then outputted from a top of the backlight 2. Another partof the scattered light, which is directed to a top of the scatteringregion 30B, is transmitted through the light guide plate 10, and thenoutputted from the top of the backlight 2.

In this way, in the embodiment, light is hardly outputted from the topof the transparent region 30A, and largely outputted from the top of thescattering region 30B. This increases luminance of a region(hereinafter, simply called scattering region in the light emittingarea) corresponding to a region having light-scattering ability(scattering region 30B) in the light emitting area of the backlight 2.As a result, a modulation ratio in a front direction is increased.

In the first embodiment, an optically isotropic material is used for thebulk 38A or 38B, and an optically anisotropic material is used for thefine particles 39A or 39B. In contrast, in the embodiment, an opticallyanisotropic material is used for each of the bulk 68A or 68B and thefine particles 69A or 69B. This may reduce a difference in refractiveindex between the bulk 68A or 68B and the fine particles 69A or 69B notonly in the oblique and lateral directions but also in the verticaldirection, leading to high transparency. Thus, since light leakage maybe reduced or substantially eliminated in the transparent region 30A,the transparent region 30A may be darkened by a level corresponding todecrease in amount of light leakage, and the scattering region 30B maybe lightened by the level. Consequently, in the embodiment, displayluminance may be increased while light leakage is reduced orsubstantially eliminated in the transparent region 30A. As a result, amodulation ratio in a front direction may be increased, and furthermore,luminance raise may be achieved without increasing input power to thebacklight 2.

In the embodiment, an occupancy rate of the first region 64A in thelight modulator layer 64 is increased with increase in distance from thelight source 20. Thus, luminance may be made uniform in a plane not onlyin a case where the whole light emitting area of the backlight 2 isdarkened, but also in a case where the whole light emitting area of thebacklight 2 is lightened. As a result, for example, when white displayis performed in an area α₁ near the light source 20 and in an area α₂away from the light source 20, white luminance may be equalized betweenboth the areas as shown in FIG. 17D. Moreover, for example, when blackdisplay is performed in an area β₁ near the light source 20 comparedwith the area α₁, in an area β₂ between the area α₁ and the area α₂, andin area β₃ away from the light source 20 compared with the area α₂,black luminance may be equalized between the areas as shown in FIG. 17D.

Application Example

Next, an application example of the backlight 1 or 2 of the embodimentis described.

FIG. 31 shows an example of a schematic configuration of a displaydevice 3 according to the application example. The display device 3includes a liquid crystal display panel 80 (display panel), and thebacklight 1 or 2 disposed in the back of the liquid crystal displaypanel 80.

The liquid crystal display panel 80 displays a picture. The panel 80 is,for example, a transmissive display panel in which each pixel is drivenaccording to a picture signal, and has a structure where a liquidcrystal layer is sandwiched by a pair of transparent substrates.Specifically, the liquid crystal display panel 80 has a polarizer, atransparent substrate, pixel electrodes, an alignment film, a liquidcrystal layer, an alignment film, a common electrode, a color filter, atransparent substrate and a polarizer in order from a backlight 1 side.

Each transparent substrate includes a substrate transparent to visiblelight, for example, sheet glass. While not shown, an active drivecircuit including TFT (Thin Film Transistor) electrically connected tothe pixel electrodes and wirings are formed on the transparent substrateon the backlight 1 side. The pixel electrodes and the common electrodeinclude, for example, ITO. The pixel electrodes are lattice-arranged ordelta-arranged on the transparent substrate, and act as electrodes foreach pixel. On the other hand, the common electrode is formed all overthe color filter, and acts as a common electrode opposed to each of thepixel electrodes. The alignment film includes, for example, ahigh-polymer material such as polyimide, and is to perform alignmentprocessing to a liquid crystal. The liquid crystal layer includes, forexample, a liquid crystal of a VA (Vertical Alignment) mode, a TN(Twisted Nematic) mode, or an STN (Super Twisted Nematic) mode, and actsto change a direction of a polarization axis of light emitted from thebacklight 1 for each pixel according to a voltage applied from a drivecircuit (not shown). Arrangement of the liquid crystal is changed inmulti levels, thereby a direction of a transmission axis for each pixelis adjusted in multi levels. The color filter includes color filtersarranged in correspondence to arrangement of the pixel electrodes, thecolor filters dividing light, which has been transmitted through theliquid crystal layer, for example, into three primary colors of red (R),green (G) and blue (B), or into four colors of R, G, B and white (W).Filter arrangement (pixel arrangement) typically includes stripearrangement, diagonal arrangement, delta arrangement, and rectanglearrangement.

Each polarizer is an optical shutter, and transmits only light(polarized light) in a certain vibration direction. While the polarizermay be an absorption polarizing element absorbing light (polarizedlight) in a vibration direction other than a transmission axisdirection, the polarizer is preferably a reflection polarizing elementreflecting light to the backlight 1 side from the point of luminanceimprovement. The polarizers are disposed such that their polarizing axesare different by 90 degrees from each other, and thus light emitted fromthe backlight 1 is transmitted through the liquid crystal layer or shutout by the liquid crystal layer.

When the backlight 1 is provided in the back of the liquid crystaldisplay panel 80, the drive circuit 50, for example, controls a level ofvoltage applied to the pair of electrodes such that a light axis of thefine particles 39A or 39B is perpendicular or approximatelyperpendicular to a reference surface in one light modulator cell 30A,and a light axis of the fine particles 39A shallowly intersect with thereference surface in the other light modulator cell 30B. When thebacklight 2 is provided in the back of the liquid crystal display panel80, the drive circuit 50, for example, controls a level of voltageapplied to the pair of electrodes such that a light axis AX2 of the fineparticles 39B is parallel to a light axis AX1 of the bulk 38A in a cellcorresponding to a position of a black display pixel in a plurality oflight modulator cells 30A, and the light axis AX2 of the fine particles39B intersects with the light axis AX1 of the bulk 38A in a cellcorresponding to a position of a white display pixel in the lightmodulator cells 30A.

In the application example, when the backlight 1 or 2 of the embodimentis used as a light source for illuminating the liquid crystal displaypanel 80, a modulation ratio may be increased while luminance is madeuniform in a plane. In addition, luminance raise may be achieved withoutincreasing input power to the backlight 1 or 2.

In the application example, the backlight 1 or 2 modulates intensity oflight partially incident to the liquid crystal display panel 80 inaccordance with a display image. However, when abrupt brightness changeoccurs at a pattern edge portion of the electrode (lower electrode 32 orupper electrode 36) included in the light modulator 30 or 60, such aboundary portion is inconveniently seen even on a display image. Thus,the backlight is demanded to have a characteristic that brightnessmonotonously changes to the utmost in an electrode boundary region, andsuch a characteristic is called gradation characteristic. While use of adiffuser plate having high diffusibility is effective to increase thegradation characteristic, when diffusibility is high, total lighttransmittance is also reduced, and therefore brightness tends to bereduced. Therefore, when a diffuser plate is used for the optical sheet70 in the application example, total light transmittance of the diffuserplate is preferably 50% to 85%, and more preferably 60% to 80%.Moreover, the gradation characteristic is improved with increase inspatial distance between the light guide plate 10 and the diffuser platewithin the backlight 1 or 2. In addition, number of patterns of theelectrode (lower electrode 32 or upper electrode 36) included in thelight modulator 30 or 60 may be increased to adjust a voltage of eachelectrode such that lightness or darkness monotonously changes to theutmost.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A method of manufacturing a light modulator, the method comprising:disposing two transparent substrates, each transparent substrate havingan electrode and an alignment film formed sequentially on its surface,such that respective alignment films are opposed to each other, andattaching the transparent substrates to each other with a mixture of aliquid crystal material and a polymerizable material in between, andthen disposing a mask on the attached transparent substrates, the maskhaving an open area ratio varying depending on a distance from a regionwhere a light source is to be disposed; and irradiating light to thepolymerizable material via the mask to polymerize the polymerizablematerial, thereby forming a first region being changed between atransparent state and a scatterable state depending on an intensity ofan electric field, and a second region being more transparent than thefirst region in a scatterable state at an electric field having acertain intensity, the electric field being applied when the firstregion is changed between the transparent state and the scatterablestate
 2. The method of manufacturing a light modulator according toclaim 1, wherein the mixture is formed by patterning a plurality ofmaterials being different from one another in weight ratio between theliquid crystal material and the polymerizable material.